Melt-out metal parts of complex shapes are made for use as cores in subsequently molded plastic components. Such cores are made of a low melting temperature alloy and are removed from the plastics components by melting the core and leaving the component. In another embodiment, metal alloys with low melting temperatures are used for encapsulating components such as turbine blades so they may be held for machining and other finishing steps. After use, the metal from the cores or encapsulations is re-melted and re-used. One example of an apparatus for casting metal alloys with low melting temperatures is disclosed in U.S. Pat. No. 4,676,296.
In the apparatus depicted in this patent, a cylinder is provided in a tank of liquid metal alloy with a passage from the bottom of the cylinder passing out through the tank and into a mold or die. A valve is provided in the passage to shut off the flow of molten metal alloy in between injection cycles. A piston moves up and down within the cylinder and the cylinder is filled by raising the piston up above a filler aperture in the top of the cylinder to allow liquid metal alloy to flow into the cylinder. Before commencing the injection step, the piston is moved downwards a predetermined amount so that the liquid metal alloy within the cylinder is pre-pressurized. After the pre-pressurization step, the valve in the passage to the die is opened to permit liquid metal alloy to be injected into the die.